The invention relates to methods of directed self-assembly and the layered structures formed therefrom, and more specifically, to the directed self-assembly of microdomains of block copolymers to produce self-assembled structures with fewer defects.
The ability to pattern features with smaller critical dimensions allows denser circuitry to be fabricated, thereby enabling more circuit elements within the same area and reducing the overall cost per element. Features having smaller critical dimensions and tighter pitch are needed in each technology generation. Directed self-assembly (DSA) of polymeric material is a potential candidate to extend current lithography by enhancing the spatial resolution and/or controlling the critical dimension variation of a predefined pattern on a substrate. In addition, the block copolymer (BCP) self-assembly process can improve the dimensional control due to the lower critical dimension variation (both mean critical dimension and line-edge roughness (LER) or line-width roughness (LWR)) in the final self-assembled structure compared to that in the pre-pattern. In particular, DSA of block copolymer (BCP) materials and polymer blends have been explored for this purpose.
In the graphoepitaxy method, the self-organization of block copolymers is guided by topographical features of pre-patterned substrates. With a trench of width L and BCP with a periodicity of PBCP, frequency multiplication of a factor of L/PBCP can be achieved. In practice, it is useful for the bottom of the trench to be comprised of an orientation control material in order to support perpendicularly-oriented domains.
Alternatively, in early forms of the chemical epitaxy method, the self-assembly of BCP materials to form domains is directed by dense chemical patterns. The pitch of the chemical pattern (PS) is roughly equivalent to the pitch of the BCP domain periodicity (PBCP). The preferential affinity between at least one of the chemical pattern regions and a corresponding BCP domain directs the self-assembly of the BCP domains in accordance with the underlying chemical pre-pattern. Unfortunately, current optical lithography tools do not have sufficient resolution to print these 1:1 chemical patterns. Instead, these patterns have been fabricated using lithographic techniques such as e-beam direct write or extreme-ultraviolet (EUV, 13.5 nm) interference lithography, which are not suitable for volume manufacturing.
Alternatively, chemical epitaxy on sparse chemical patterns can provide critical dimension and orientation control similar to that achieved on dense chemical patterns while also providing enhanced resolution. For example, the directed self-assembly of BCP material can form domains on a sparse chemical pattern layer comprised of alternating pinning regions having a width WP=0.5*PBCP and regions with an orientation control material having a width WCA=PS−WP. An orientation control material having an operationally equivalent affinity for both domains is used to support perpendicularly-oriented domains. The factor of frequency multiplication is determined by the ratio of the pitch of the sparse chemical patterns stripe (PS) and the pitch of BCP (PBCP). A ratio of PS/PBCP=2 would result in frequency doubling and a ratio of PS/PBCP=3 would result in frequency tripling. In practice, it has been shown that the defect levels observed in the DSA of block copolymers via chemical epitaxy on sparse chemical patterns increase with the factor of frequency multiplication.